This invention relates to a motor controller and control method.
When controlling the rotation of a brushless motor such as a permanent magnet type synchronous motor, a sensor is required which detects a rotor phase because the current led to a stator coil is controlled according to a rotation angular position of the rotor (rotor phase).
One example of such a sensor is a resolver which has a high resolving power. However, since the resolver is expensive, a more economical sensor is desired even if its resolving power is low.
In the controller disclosed by JP-A-H9-74790 published in 1997 by the Japanese Patent Office, the resolving power of the sensor is decreased to an electrical angle of 60 degrees, and finer rotor phase are detected by performing an interpolation computation.
However, to perform this interpolation of rotor phase, the rotor must rotate above a certain speed. Therefore, during startup when the rotor rotation speed is zero or at very low rotation speeds, the correct rotor phase is not obtained, so it is impossible to control the current supplied to the motor to the optimum level, and the torque of the motor decreases.
It is therefore an object of this invention to obtain sufficient motor torque even when the motor starts or when it is rotating at low speed, by changing over the mode of current supply to the motor.
It is a further object of this invention to suppress a sudden change of motor torque when the control mode is changed.
In order to achieve above object, this invention provides a control device for controlling current supplied to a motor, comprising a phase sensor which detects a rotor phase of the motor at a predetermined angular resolution, and outputs a phase signal corresponding to plural phase determination ranges, a drive device which drives the motor, and a controller.
The controller functions to select one method from plural methods for determining a current control rotor phase from the phase signal, determine the current control rotor phase from the phase signals using the selected method, compute a command value of the current supplied to the motor using the determined current control rotor phase, and output the command value of the current to the drive device.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.